An example of conventional organic EL devices is disclosed in JP-A-7-78689. The organic EL device disclosed in this patent application has an objective of obtaining high luminescent brightness. This EL device is characterized in that the wavelength of an interference peak (A2) is coincided with the wavelength of a intensity peak (B2) of light produced in an organic light-emitting layer as shown in FIG. 20. Specifically, an interference effect occurs when light produced in an organic light-emitting layer passes through several thin film layers. The objective of the invention of the above-described patent application is to accord the wavelength of the interference peak due to this interference effect with the wavelength of the intensity peak for light produced in the light-emitting layer.
However, if the interference peak wavelength due to the interference effect is coincided with the intensity peak wavelength, a tendency for a color purity (CIE chromaticity coordinates) decrease is experienced. For example, a blue light of organic EL device with a intensity peak wavelength in the range of 400 to 490 nm includes green light components with a high luminous efficacy. If the interference peak wavelength is coincided with the intensity peak wavelength, the intensity of the green light components is also increased, resulting in a tendency for a decrease in the color purity (CIE chromaticity coordinates).
Also, JP-A-7-240277 discloses an organic EL device in which the total optical thickness of high refractive index transparent electrodes and organic light-emitting layers is designed so as to increase the center wavelength value.
However, in this organic EL device, a color purity decreases because an increase in the center wavelength value also entails an increase in the intensity at neighborhood of the center wavelength.
A constant CIE color coordinate value can be obtained if the thickness of the organic light-emitting layers is definitely uniform and does not fluctuate any more. However, this is not practical because such an organic light-emitting layer can be produced only at the extreme sacrifice of production yield.
As a result of extensive studies to solve these problems, the inventors of the present invention have found the following things, namely, the CIE chromaticity coordinate values which is measured in accordance with JIS Z 8701, periodically varies with peaks and valleys corresponding to the total optical path length of a transparent electrode and an organic layer. Thus, a change in the CIE chromaticity coordinate value can be decreased if the thickness of the organic layer is determined taking the values for such peaks and valleys into consideration so that the interference peak wavelength and the intensity peak wavelength are staggered to a certain extent.
Specifically, an object of the present invention is to provide an organic EL device exhibiting only a slight change in the color purity (CIE chromaticity coordinates) even if the total optical path length of a transparent electrode and an organic layer changes in a prescribed range, and a method of efficiently manufacturing such an organic EL device.